Researchers examine climate change impact on water supplies

WASHINGTON, D.C. and COLUMBUS, OHIO—Researchers are evaluating the impact of climate change on the nation’s drinking water supply. The Awwa Research Foundation (AwwaRF) began sponsoring research to assess and plan responses to the impacts of climate change as early as 2003. The studies are summarized in the 2006 report, Climate Change and Water Resources: A Primer for Municipal Water Providers.

Research conducted on behalf of the AwwaRF’s 900 water utility members concludes that among the first and most critical impacts of climate change will be changes to precipitation patterns around the world during this century, which will directly affect the availability of drinking water.

Water utilities are concerned that extended changes in precipitation will lead (and have already led) to extended droughts. Climate change is also generating greater intensity of rainfall, which will increase erosion, flooding, and difficulty capturing excess water for storage. Storage capacity is inadequate for quantities that will be needed for use over longer periods than in the past.

The AwwaRF reported the following key conclusions:

Global rain and snowfall will likely increase as temperatures rise, but not uniformly across the planet. Such variation makes contingency planning difficult.

Global precipitation will likely be less frequent but more intense, leading to risk of flooding.

As the globe warms, more precipitation will fall as rain, rather than snow. Snow packs will decline, and warmer temperatures will begin the melt season earlier. Rain will replace snow, and rain falling on snow sets the stage for greater winter and spring runoff and a risk of floods.

As temperatures rise, periods of drought will increase. Droughts lead to a greater likelihood of forest fires as an earlier loss of snowpack, drier summer soils, and stressed trees become fodder for fires.

Rising temperatures are expected to lead to rising sea levels, which impact coastal area water quality.

The impact to coastal areas is addressed in a new study from The Ohio State University (OSU), which concludes that as sea levels rise, coastal communities could lose as much as 50 percent more of their fresh water supplies than previously thought. Hydrologists simulated how saltwater will intrude into fresh water aquifers, given the sea level rise predicted by the Intergovernmental Panel on Climate Change (IPCC), which concluded that within the next 100 years, sea level could rise as much as 23 inches, flooding coasts worldwide.

Scientists previously assumed that, as saltwater moved inland, it would penetrate underground only as far as it did above ground. But this new research shows that when saltwater and fresh water meet, they mix in complex ways, depending on the texture of the sand along the coastline. In some cases, a zone of mixed, or brackish, water can extend 50 percent further inland underground than it does above ground.

"Climate change is already diminishing fresh water resources with changes in precipitation patterns and the melting of glaciers," said Motomu Ibaraki, associate professor of earth sciences at OSU, who led the study. "With this work, we are pointing out another way that climate change can potentially reduce available drinking water. The coastlines that are vulnerable include some of the most densely populated regions of the world."

Scientists have used the IPCC reports to draw maps of how the world’s coastlines will change as waters rise. Ibaraki said that he would like to create similar maps that show how the water supply could be affected. However, that’s not an easy task because scientists don’t know exactly where all of the world’s fresh water is located, or how much is there. Nor do they know the details of the subterranean structure in many places.

One finding of the OSU study is that saltwater will penetrate further into areas that have a complex underground structure. Typically, coastlines are made of different sandy layers that have built up over time, Ibaraki explained. Some layers may contain coarse sand and others fine sand. Fine sand tends to block more water, while coarse sand lets more flow through.

Researchers simulated coastlines made entirely of coarse or fine sand, and different textures in between. They also simulated more realistic, layered underground structures. The simulation showed that, the more layers a coastline has, the more the saltwater and fresh water mix. The mixing causes convection—similar to the currents that stir water in the open sea. Between the incoming saltwater and the inland fresh water, a pool of brackish water forms. Further sea level rise increases the mixing even more. Depending on how these two factors interact, underground brackish water can extend 10 to 50 percent further inland than the saltwater on the surface.

The AwwaRF and its members are examining a number of other critical issues related to climate change. Current research underway looks at the following:

mitigating increasing damage to watersheds and water quality through extreme events such as wildfires and hurricanes;

creating new sources of water through water recycling and desalination;

conducting research to understand the public’s concerns about water reuse;

helping water utilities reduce greenhouse gas emissions;

examining how water providers/utilities meet the public’s demand and need for water by examining water conservation and water-saving technologies;